European Medicines Agency Veterinary Medicines and Inspections EMEA/CVMP/2316/2005-FINAL January 2005 COMMITTEE FOR MEDICINAL PRODUCTS FOR VETERINARY USE THIAMPHENICOL (Extension to pigs) SUMMARY REPORT (5) 1. Thiamphenicol (CAS: 15318-45-3) is a broad–spectrum antibiotic closely related to chloramphenicol. The chemical structure of thiamphenicol differs from that of chloramphenicol in having a sulpho-group instead of a nitro-group. Thiamphenicol is active against both Gram- negative and Gram-positive bacteria, and is especially active on anaerobes. Thiamphenicol is used for the treatment and control of respiratory and intestinal infections in cattle and poultry by oral or intramuscular administration. The substance is also used for intramammary administration in both lactating and dry cows and for intrauterine administration in cows. A microbiological ADI of 2.5 µg/kg bw i.e. 150 µg/person was previously established for thiamphenicol based on microbiological effects on human gut flora. Currently, thiamphenicol is included in Annex I of Council Regulation (EEC) No 2377/90 as follows: Pharmacologically Marker residue Animal MRLs Target Other provisions active substance(s) species tissues Thiamphenicol Thiamphenicol Bovine 50 µg/kg Muscle 50 µg/kg Fat 50 µg/kg Liver 50 µg/kg Kidney 50 µg/kg Milk Chicken 50 µg/kg Muscle Not for use in 50 µg/kg Skin+fat animals from which 50 µg/kg Liver eggs are produced for 50 µg/kg Kidney human consumption Provisional MRLs had also been previously established for pigs, ovines and fin fish, with a value of 50 µg/kg for all relevant tissues, however final MRLs could not be recommended for these species due to the inadequate information on the ratio marker to total microbiologically active residues and the absence of a fully validated analytical method for monitoring residues in edible tissues. A new application has now been submitted for the extension of the current MRLs for thiamphenicol to pigs, including new data to establish the ratio of marker to total residues as well as a new analytical method. New data on the metabolism of thiamphenicol in pigs were also included. In pigs, thiamphenicol is intended for the treatment of respiratory and intestinal infections with a recommended dose of 30 mg/kg bw orally, intramuscularly or intravenously for up to 5 days. 7 Westferry Circus, Canary Wharf, London, E14 4HB, UK Tel. (44-20) 74 18 84 00 Fax (44-20) 74 18 84 47 E-mail: [email protected] http://www.emea.eu.int EMEA 2005 Reproduction and/or distribution of this document is authorised for non commercial purposes only provided the EMEA is acknowledged 2. Fifteen pigs were treated orally twice a day for 5 days with 10, 15 or 20 mg/kg bw thiamphenicol. Blood samples were analysed by gas chromatography with electron capture detector (limit of quantification 20 µg/l). For unchanged thiamphenicol, the samples were extracted in organic phase without enzyme hydrolysis, for the total thiamphenicol the samples were incubated with beta-glucurase before analysis. Thiamphenicol was rapidly absorbed and the area under the curve and Cmax of unchanged thiamphenicol were linearly correlated with the dose. No accumulation of thiamphenicol or thiamphenicol glucuronide was evident in swine plasma after oral administration at doses of 10, 15 and 20 mg thiamphenicol/kg bw twice daily for 5 consecutive days. In a GLP study, 16 pigs were fed twice daily with 900 mg thiamphenicol/kg feed (approximately 30 mg/kg bw/day) for 5 days; 3 pigs were maintained as controls. Thiamphenicol was measured in plasma following solvent extraction, using a solid-phase liquid-liquid partitioning technique and HPLC (limit of detection 0.01 µg/ml). The maximum mean level of thiamphenicol in plasma (1.28 µg/ml), was found at 8 hours after the first dose administration. Six healthy male pigs were treated with medicated water containing 2.5 ml of 10% thiamphenicol/l of water, ad libitum, for 5 days. Peak plasma concentration (mean plasma concentration at the steady state 1.01 ± 0.44 µg/ml) was reached at 36 hours after the start of treatment and the levels remained similar until the end of the treatment period (120 hours). Elimination half live (2.9 ± 0.3 hours) was determined by linear regression of the terminal phase, when treatment was stopped. Administration of thiamphenicol in water resulted in an increase in plasma levels until the peak and steady state concentration was reached at approximately 36 hours after start of administration. Elimination of thiamphenicol from plasma was rapid upon cessation of treatment. Pharmacokinetic parameters of thiamphenicol were determined after single intravenous or intramuscular administration of 30 mg/kg bw to 5 male pigs. Three weeks later, the same animals were administered a second dose via the other route. Plasma thiamphenicol concentrations were determined by HPLC (limit of quantification 20 ng/ml). Intravenous thiamphenicol kinetics were fitted to a bi-exponential equation, with a first rapid disposition phase followed by a slower disposition phase. The thiamphenicol elimination half-life following intramuscular administration was statistically greater than following intravenous administration, probably due to the slow rate of absorption from the muscle. Six Large White male pigs (26.6 ± 4.1 kg) were administered a single dose of 30 mg/kg bw/day thiamphenicol intravenously. A validated HPLC analytical method with UV detection was used to determine thiamphenicol concentration in plasma. The limit of quantification of the method was 0.02 µg/ml. The linearity of the method was determined between 0.02 µg/ml and 15 µg/ml; precision and accuracy were below 15 %. Elimination half life was short (1.2 ± 0.5 h) and there was a high rate of plasma clearance (356.4 ± 119.7 ml/min). Three female and 3 male pigs (body weight 27 to 34 kg) were administered either 10 mg/kg bw (as solution by intravenous route) or 30 mg/kg bw (as suspension by oral route). Three weeks later the animals were administered thiamphenicol by the alternative route. Serum concentrations of thiamphenicol were determined by a validated HPLC analytical method (limit of quantification 0.05 µg/ml). The short elimination half-life and mean residence time values following intravenous administration confirms the rapid elimination of thiamphenicol in pigs compared with oral administration. 2/8 EMEA 2005 Pharmacokinetics of unchanged thiamphenicol and thiamphenicol glucuronate were determined in 4 pigs administered thiamphenicol orally at 30 mg/kg bw in the feed and thiamphenicol intravenously at 10 mg/kg bw as glycinate, following a cross-over design. Both free and total thiamphenicol were assayed in plasma and urine samples, according to GLP requirements, using a validated HPLC-UV method (limit of quantification 0.021 µg/ml for plasma and 0.21 µg/ml for urine). Concentrations of glucuronate thiamphenicol were determined by subtracting the quantity of free thiamphenicol from that of total thiamphenicol. In urine, highest concentrations of total thiamphenicol occurred 4 hours after oral administration and ranged between 610 and 723 mg/l. After intravenous administration, maximum urine concentrations also occurred after 4 hours with a range of 363 to 1136 mg/l. The area under the curve after oral administration for total thiamphenicol is about 4 times that of free thiamphenicol. Following intravenous administration, this ratio is only 2 times, suggesting that glucuronidation after oral administration is much higher than after intravenous administration. For total thiamphenicol, the average elimination ratio, half life and distribution volume are similar in both routes of administration. Elimination parameters of free thiamphenicol are similar for the 2 routes of administration. In a GLP study, thiamphenicol was administered to 2 groups of 4 pigs each. One group was treated orally at a dose rate of 30 mg/kg bw of thiamphenicol, once daily for 3 consecutive days. The other group was administered thiamphenicol intramuscularly at a dose rate of 30 mg/kg bw once daily for 3 consecutive days. After a washout period of 11 days animals in the first group were administered thiamphenicol intramuscularly and those in the other group received thiamphenicol in the feed. After intramuscular administration, blood samples were taken at 0, 0.25, 0.5, 1, 2, 6 and 12 hours after the first administration, 0, 1 and 12 hours after the second administration and 0, 1, 12, 24, 36 and 48 hours after the third administration. Following oral administration, blood samples were taken at 0, 0.5, 1.5, 3, 5, 7 and 12 hours after the first administration, 0, 1.5 and 12 hours after the second administration and 0, 1.5, 12, 24, 36 and 48 hours after the third administration. Determination of thiamphenicol in plasma was carried out using an HPLC/MS/MS analytical method fully validated in the range 0.20 to 20.00 µg/ml; the limit of quantification and limit of detection were 0.20 and 0.05 µg/ml, respectively. The results show a rapid absorption following both routes of administration though intramuscular administration leads to a higher plasma concentration and a higher bioavailability following intramuscular administration. The relative bioavailability of the oral route to the intramuscular route was approximately 48%. The elimination half lives were comparable for the two routes of administration. The absence of difference in plasma concentrations achieved after the first, second or third day demonstrated absence of accumulation for each of the routes of administration tested. 3. In a GLP study 32 pigs were administered daily 30 mg thiamphenicol/kg bw intramuscularly for 5 days. Groups of 2 males and 2 females were slaughtered at either 8 hours, 1, 4, 8, 15, 21 or 28 days after treatment. Administration was made into the left side of the neck on days 1 to 4 and into the right side of the neck on day 5.